The invention relates to a solar module with border sealing having the characteristics of the preamble of claim 1.
Document DE 195 14 908 C1 discloses a process for manufacturing a solar module, in which a polyether-polyurethane is used as a casting substance for sealing a thin-film solar cells embedded between two glass panes.
Once the solar cells have been fixed to a support plate, the electrical connections between the individual solar cells (series circuit) are made and the leads grouped in rows are brought to the outside at predetermined places over the edge of the glass support plate. An adhesive bead is then deposited, for example by extrusion, along the edge of the pane, which bead serves, on the one hand, to seal the border of the solar modular and, on the other hand, to act as a spacer between the two glass plates. Nothing is mentioned about the composition of the adhesive bead, apart from its ability to be extruded, nor is anything mentioned about the type of construction of the solar cells.
Introduced into two diagonally opposed corner regions of the adhesive bead are lengths of tubing which serve for the subsequent filling and venting of the hollow space between the two glass panes. Next, the front glass pane is applied and then the two glass panes are compressed, one against the other, until the desired spacing is achieved.
Next, the hollow space between the two glass panes is filled with the casting resin compound, the solar module preferably being oriented in a roughly vertical position and the casting resin substance filling the space via a lower tube, while the upper tube serves for venting. After filling, the two tubes are removed and the orifices are sealed using an adhesive.
The solar module thus filled without any bubbles forming is then put into an autoclave. The temperature of the autoclave is about 40xc2x0 C. and the overpressure in the autoclave is set to about 0.6 bar. Under these conditions, the casting resin cures and, after 60 minutes, reaches the completely cured state. After removing the solar module from the autoclave, it is ready to be used. In practice when manufacturing such a solar module, it is also possible to dispense with the overpressure.
A widely-practised method of constructing solar cells is to use a layer of absorbent containing, as constituents, copper, indium and selenium, and sometimes also sulphur instead of selenium (this is known as a CIS absorbent layer). It is also possible to add gallium to the absorbent layer (hence a CIGS absorbent layer). In general, and hereafter, these layers will be called chalcopyrite absorbent layers. It is known that their photovoltaic yield is appreciably reduced by the penetration of moisture, or alternatively the penetration of water molecules by diffusion, even without a visible deterioration in the optical appearance.
In the case of the above solar modules, of the type mentioned at the start, having a chalcopyrite absorbent layer, an acrylic tape (commercially available with the name 3M Isotac 4918) is used as a border seal. It turns out that the solar cells provided with this seal, after undergoing the damp-heat test according to the IEC 61215 standard (IEC=International Energy Commission), were admittedly impeccable from the optical standpoint, but their yield had dropped by more than 20% as a result of water molecules defusing into the chalcopyrite absorbent layer. However, according to the IEC 1646 standard, only a reduction of 5% is allowed.
The damp-heat test mentioned essentially consists of storing the solar modules for more than 1000 hours at a temperature of 85xc2x0 C. and a relative humidity of 85%. It turns out that penetration of water molecules by diffusion rapidly increases with the duration of use.
In this context it is known (Document DE 197 33 913 A1), for the purpose of producing an environmentally resistant encapsulation of thin-film structural elements, for example solar modules with a chalcopyrite absorbent layer, to fill a hollow space formed between a frame and the border of the structural element using a drying agent for the purpose of absorbing moisture. This is in fact to avoid turbidity brought about by the moisture in the laminated adhesive used and corrosion of the bands of solder conducting the current for external electrical contacting of the modules.
According to document DE 195 03 510 C2, it is possible to seal around the border of the composite glass panes which are provided with a heat-reflecting coating, which is embedded in the composite, by not extending the coating as far as the external edge and by sealing the peripheral slot around the border between the two glass panes using a polymer introduced by spraying, which polymer may be combined, by melting, with the polymer of which the composite is formed.
It is also known (from document DE 41 31 393 C2) to provide the internal faces of the individual panes with an isolating pane made of conventional solar cell glass, the electrical connections of which are taken beyond the border composite out of the gas-tight sealed internal space. The border composite is composed there of a spacer, its bonding to the glass panes and of a seal of a conventional kind placed on the outside. This publication also describes solar cells embedded in a casting resin, which are also protected by a border seal against the effects of the external environment. However, the composition of this seal is not specified further.
In order to seal the disk-shaped intermediate spaces of the glass isolating panes, it is known to introduce a drying agent such as a moisture absorbent into the spacer, which may be manufactured from an adhesively bonded metal section or from a bead of elastomer. The drying agent is also called a molecular sieve.
If the spacer is only made from an elastomer (xe2x80x9cthermoplastic spacerxe2x80x9d or TPS for short), the drying agent is mixed with the synthetic material before application (for example before extrusion) to the edge of the glass pane. A commercial compound (the product Naftotherm(copyright) BU-TPS from Chemetall GmbH) for a thermoplastic spacer is composed of polyisobutylene as base and of zeolite powder as drying agent. This material with a component, containing no solvents, can be extruded in the range of about 140 to 160xc2x0 C. and adheres well to glass.
The basic objective of the invention is to indicate a further improved seal for a thin-film structural element with a chalcopyrite absorbent layer.
This objective is achieved according to the invention by means of the characteristics of claim 1. The characteristics of the secondary claims indicate advantageous improvements to this article.